A plug-in hybrid electric vehicle has the capability to operate significant distances in pure electric mode, without running the engine to recharge the battery. It is commonly assumed that a plug-in hybrid electric vehicle would run the engine only when necessary to recharge the battery. This may be a good strategy if electricity is much cheaper than gasoline. But it may be desirable to start the engine periodically, regardless of any need for battery charging. For example, some customers may take mostly short trips, and may consistently plug in the vehicle between trips, such that the engine is almost never needed for battery charging.
Long periods of engine inactivity could cause a variety of problems, including water condensation, corrosion, air leakage into hydraulic valvetrain components and/or into the fuel system, oil and/or coolant leakage past rotating seals, “stale” fuel, etc. To avoid these problems, the engine should be started and operated periodically even when it is not required for battery recharging.
The inventors herein have recognized that starting the engine at times other than low battery state of charge may concern the driver as they are not aware of the reason for the engine starting.
In one approach a method is provided for controlling a plug-in hybrid vehicle having an engine, the method carried out by a control system. The method may comprise during a first engine stopped condition, performing a first start of the engine in response to a battery state of charge, where the engine is started during a first state of charge; during a second engine stopped condition, performing a second start of the engine in response an operating parameter, where the engine is started during a second state of charge, the second state of charge higher than the first state of charge; delaying the performing of the second start until a selected event occurs; and performing a first stop of the engine in response to the battery state of charge, where the engine is stopped during a third state of charge higher than the first and second states of charge.
The selected conditions may include conditions that mask engine starting and/or continued engine operation, but that also effectively utilize engine output even if battery state of charge is sufficiently high, such as high vehicle speeds, vehicle acceleration, etc. Further, other selected conditions may also be used, such as if the vehicle is traveling on rough roads, high stereo volume in the vehicle, or others, and/or combinations thereof.
In this way, engine starts may be used to address potential degradation that may occur, even if the state of charge does not require engine operation; yet, a high driver perception can be maintained by appropriately delaying the start until the selected conditions occur.
Thus, by delaying the starting of the second, higher state of charge, engine start until the selected conditions are present, it may be possible to better mask the potentially unexpected start from the driver. Additionally, or alternatively, it may be possible to have the engine start repeatedly correlate to consistent conditions so that the driver comes to expect the engine start, even though the battery state of charge is higher than other engine starts.
Note that as used above, the first engine start may occur later in time than the second engine start, or vice versa, and each may occur in a common drive cycle of the vehicle. Further, the first and second engine starts may not occur immediately following one another, and there may be various additional starts occurring before, after, and/or between them.
In another example, a method includes, during vehicle operation, starting and stopping the engine in response to a battery state of charge, where the engine is started during a first state of charge and stopped during a second, higher, state of charge; and requesting a vehicle operator to start the engine in response to selected engine off conditions.
In this way, the operator can exert some control on engine starting to either improve drive feel, and/or to accommodate information only the operator may have, such as how long the drive cycle will last, how far the vehicle will travel in the drive cycle, and/or intended plans for vehicle recharging. However, if the operator fails to initiate the engine for sufficient duration, the method may further include starting the engine even without receiving a driver request to start the engine.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.